Born in Gainford in County Durham, the son of Thomas Macknight, and his wife, Elizabeth, Macknight was privately educated at Dr Bowman's school in Gainford.
The Liberal Unionist editor of the Belfast Norther Whig, Thomas Macknight, who had been a personal friend of O'Hagan, states in his memoir ULSTER AS IT IS (London, 1896) that he believed O'Hagan would have opposed Gladstone's conversion to Home Rule had he not died when he did.
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